This invention relates to the art of environmental control systems, to the art of thermostats which control heating, ventilation and cooling systems, and more particularly to those thermostats which incorporate a motion detector or occupancy sensor. Additional related fields of art include electric heating, electric heaters, electric baseboard heaters, air-conditioning system control, thermostats, energy conservation, energy management, motion detectors, and occupancy sensors. Heating Ventilation and/or Air Conditioning systems are commonly referred to as HVAC units, or just HVAC.
Energy usage for environmental control, especially for heating or cooling, is a major expense in many homes and businesses. Even minor changes in environmental control procedures can result in significant energy savings. Typical approaches for saving energy include such procedures as manually turning off a heating or cooling system when a room is not used, or reducing the level of heating or cooling based upon some algorithm of programmed control in a thermostat. It is common for example in thermostats intended for home use to provide programmable features allowing for temperature settings that are dependent upon the time of day, and also upon the day of the week with the desired temperature being set based upon the user's prediction of needs for heating or cooling, or possibly to shift energy usage to a time of day or day of the week when energy costs are lower.
Designers of thermostats have also incorporated an occupancy sensor, or provided for input from an occupancy sensor to inform the controlling mechanism for a thermostat when the conditioned space served by space conditioning equipment (a heating, cooling, and/or ventilation system) is “unoccupied” meaning that no people (or animals) are detected, presumably in the conditioned space, by the occupancy sensor. Occupancy sensors can be implemented using various types of motion detectors, such as infrared motion detectors, or could be implemented with other mechanisms for sensing presence of a person in a room, or for sensing entry of a person into a room or conditioned space. The mechanism for sensing occupancy may however not be perfectly accurate. That is, a person may be in the conditioned space served by a heating, cooling or ventilation system, and potentially not be detected by an occupancy sensor, or at least not detected for some period of time. This might be caused by a chosen mechanism for sensing occupancy which is not sensitive enough, or a person might be hidden from the “view” of the occupancy sensor. For example, in a motel room with a single thermostat incorporating a single occupancy sensor, a person might remain undetected if he were in the bathroom or had positioned himself such than an object was between him and the occupancy sensor. If this situation continued for some extended period, the mechanism for determining occupancy might decide the room was unoccupied when in reality it actually was occupied. Various scenarios that might cause an error such as this might be possible.
In a motel room it is desirable to conserve energy while still providing for comfort throughout the day and night. If a heater or air-conditioner were erroneously turned off, it could possibly cause discomfort to a guest, especially at night when the temperature might become quite uncomfortable before the guest awakes enough to correct it. In a motel room, even just mild discomfort might be something that is quite undesirable to the business.
The possibility of wrongly determining a nonoccupancy condition might occur more often during certain periods of the day. For example, at night when a person is sleeping very soundly, the person might not move for an extended period and it would become more likely to remain undetected by the occupancy sensor. This condition, for example, might be determined by the motel operator to be much more likely to happen at night, such as when a person is covered by blankets which might hinder a motion detector from sensing movement.